Amplification system having mask detection

ABSTRACT

A method and apparatus reduce the out-of-band frequency components of an RF amplified signal, preferably a CDMA signal, which has a carrier frequency which is not known in advance. The apparatus and method feature locating the frequency of the incoming signal by examining an RF output signal having both in-band frequency components and out-of-band frequency components. Typically the output signal is generated using a high-power, Class A/B amplifier. Once the frequency of the carrier has been determined, the out-of-band components are used to generate control signals which, in, for example, a feedback or feedforward circuitry, reduce the energy of the out-of-band signals and thereby provide a more linear amplifier transfer function.

BACKGROUND OF THE INVENTION

This invention relates generally to amplification systems and moreparticularly to methods and apparatus for reducing distortion inamplifiers used in such systems.

As is known in the art, amplifiers have a wide variety of applications.Amplifiers can be biased to operate in one of a number of so-calledClasses. When biased to operate in Class A, the amplifier provides alinear relationship between input voltage and output voltage. Whileoperation in Class A has a wide range of applications, when higher poweroutput and efficiency are required or desired, the amplifier issometimes biased to operate in Class A/B. When biased to operate inClass A/B, however, the Class A/B amplifier power transfer curve 10 isless linear than for Class A amplifiers, illustrated in FIG. 1 by trace14. To increase efficiency, communication systems often operateamplifiers in the non-linear region 12. This practice, however, doesintroduce amplitude and phase distortion components into the outputsignal produced by the amplifier.

As is also known in the art, most communication systems have FCCallocated frequency bandwidths 18 (that is, in-band frequencies)centered about a carrier frequency 20 as shown in FIG. 2A. For example,a CDMA (Code Division Multiple Access) communication system signal has apredefined bandwidth of 1.25 MHz. Different CDMA communication channelsare allocated different bands of the frequency spectrum. Amplifiers areused in such systems, and are frequently biased to operate in Class A/B.Referring to FIG. 2B, signal processing such as amplification by anamplifier operating in the non-linear region 12 (FIG. 1) can producedistortion frequency "shoulders" 22a-22b outside a signal's allocatedbandwidth 18. (These are called out-of-band frequencies.) Thesedistortion frequency components 22a-22b can interfere with bandwidthsallocated to other communication signals. Thus, the FCC imposes strictlimitations on out-of-band frequency components.

Many techniques exist to reduce out-of-band distortion. One suchtechnique is shown in FIG. 3 where a predistortion unit 24 is fed by asignal 25 to be amplified. The predistortion unit 24 has a powertransfer characteristic 24a (FIG. 1) and compensates for distortionintroduced by subsequent amplification in Class A/B amplifier 26. Moreparticularly, the predistortion unit 24 transforms electricalcharacteristics (for example, gain and phase) of the input signal suchthat subsequent amplification provides linear amplification to the phaseand frequency characteristics of the input signal. The predistortionunit 24 is configured with a priori measurements of the non-linearcharacteristics of the Class A/B amplifier. Unfortunately, the amplifiercharacteristics (amplification curve 10 with region 12 of FIG. 1) changeover time and temperature making effective predistortion more difficult.For example, as the temperature of the amplifier increases, itsnon-linear region 12 may become more or less linear, requiring acompensating change in the transform performed by a predistortion unit24. Some adaptive predistortion systems use look-up tables to alterpredistorter characteristics based on environmental factors such astemperature. These look-up tables include predetermined predistortercontrol settings for use in predetermined situations. However,environmental factors alone do not determine the alterations in anamplifier's characteristics. Thus, over time, amplifier characteristicsvary unpredictably due to aging of amplifier components.

Another approach to reduce amplifier distortion is to use feedforwardcompensation, as shown in FIG. 4. Here, a feedforward network 31 isincluded for reducing out-of-band distortion. The feedforward network 31includes a differencing network or combiner 30, a main amplifier 33operating as a Class A/B amplifier, an error amplifier 32, delaycircuits 28 and 28a, and a combiner 29. The differencing network 30produces an output signal representative of the difference between aportion of the signal fed to the amplifier 33 operated Class A/B and thesignal fed to the amplifier 33 prior to such amplification. Thefrequency components in the differencing network 30 output signal are,therefore, the out-of-band frequency components 22a-22b introduced byamplifier 33. Amplifying and inverting the output produced by thedifferencing network 30, by error amplifier 32, produces an out-of-bandcorrecting signal. More particularly, the combiner 29 combines thecorrecting signal produced by differencing network 30 and amplifier 32,with the delayed signal output of amplifier 31 thus reducing the energyin the out-of-band frequencies 22a-22b (FIG. 2B) of the signal output byamplifier 33. Feedforward network 31 includes delay line 28 tocompensate for the delay in error amplifier 32. It should be noted thatminute differences in timing between these elements can impair theeffectiveness of a feedforward system. While a manufacturer cancarefully match components prior to shipment, as feedforward componentsage, the correcting signal and processed signal can become mistimed ifnot properly compensated.

SUMMARY OF THE INVENTION

The invention relates to an apparatus and method for reducingout-of-band frequency components of an RF signal having a carrierfrequency which is not known in advance. The RF signal has both in-bandfrequency components and out-of-band frequency components. The apparatusfeatures a network for amplifying an input signal for producing the RFsignal, the network having adjustable electrical characteristics, and acontrol system connected to the network for locating a frequency withinthe bandwidth of the RF signal and for detecting energy in theout-of-band frequency components for producing a control signal relatedto the energy in the out-of-band frequency components. The controlsignal is coupled to the network to adjust the electricalcharacteristics of the network to reduce the energy in the out-of-bandfrequencies.

In a preferred embodiment of the invention, the network has apredistorter having adjustable characteristics controlled by the controlsignal. In another aspect, the network can include a power amplifierhaving adjustable characteristics controlled by the control signal. Inthis instance, at least one adjustable characteristic is a bias pointparameter of the amplifier. The network, in other aspects, can include afeed forward network and the signal can be, for example, a CDMA signal,having well known characteristics.

The method of the invention features locating an in-band frequencycomponent of the RF signal, detecting energy at frequencies which are ata predetermined offset from the located in-band frequency component, andadjusting network electrical characteristics to reduce the out-of-bandfrequency energy.

In particular aspects, the method features measuring the energy at afirst frequency, measuring the energy at a second frequency, anddetermining whether the energy measured at the second frequency exceedsthe energy measured at the first frequency by more than a selectedthreshold. In particular aspects, the method heterodynes the signalhaving out-of-band frequencies to baseband.

In one particular aspect of the invention, the apparatus includes apredistorter connected to receive its input signal and having its outputcoupled to a power amplifier. The predistorter has a nonlinear outputsignal versus input signal transfer characteristic which can beselectably adjusted in accordance with an out-of-band feedback controlsignal provided by a feedback loop. The result is a substantially linearamplifier output versus input signal power transfer characteristic. Thefeedback loop, in this embodiment, has a control signal connected to thepower amplifier output for locating the carrier frequency of the inputsignal and for producing a feedback control signal related to the energyin the distortion frequency components outside the bandwidth of theinput signal. The feedback control signal is coupled to the predistorterfor adjusting the electrical characteristics of the predistorter toreduce the energy in the out-of-band frequency components in the poweramplifier output.

The method and apparatus thus advantageously reduce distortion in anamplified RF signal, for example, where a Class A/B RF amplifier is usedfor efficiency and high power output.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the following drawings, in which:

FIG. 1 is a graph illustrating amplifier output regions according to thePRIOR ART;

FIGS. 2A and 2B are diagrammatical sketches of a signal having in-bandand out-of-band frequency components according to the PRIOR ART;

FIG. 3 is a diagrammatical sketch of an amplification system accordingto the PRIOR ART;

FIG. 4 is a diagrammatical sketch of another amplification systemaccording to the PRIOR ART;

FIG. 5 is a diagrammatical sketch of an amplification system having apredistorter with adjustable electrical characteristics according to theinvention;

FIGS. 6A-6C are diagrammatical sketches of frequency spectra of signalsproduced in the amplification system of FIG. 5;

FIG. 7 is a diagrammatical sketch of the amplification system of FIG. 5,a control system of such amplification system being shown in moredetail;

FIG. 8 is a flow chart of the process used by the control system in FIG.7 to produce control signals based on energy in out-of-band frequencycomponents;

FIG. 9 is a flow chart of the process used by the control system of FIG.7 to determine frequency components of a signal produced in theamplification system of FIG. 7;

FIG. 10 is a diagrammatical sketch of an amplification system having apredistorter with adjustable electrical characteristics according toanother embodiment of the invention;

FIG. 11 is a diagrammatical sketch of a mixer configured as a fourquadrant multiplier biased into a linear operating region, such mixerbeing adapted for use in the amplification system of FIG. 10;

FIG. 12 is a diagrammatical sketch of the amplification system of FIG.10, a control system of such amplification system being shown in moredetail;

FIG. 13 is a diagrammatical sketch of an amplification system accordingto another embodiment of the invention, such amplification system havinga cancellation network configured to increase dynamic range ofout-of-band signal components;

FIG. 14 is a diagrammatical sketch of an amplification system, suchamplification system having a cancellation network configured toincrease dynamic range of out-of-band signal components according toanother embodiment of the invention;

FIG. 15 is a diagrammatical sketch of an amplification system, suchamplification system having a cancellation network configured toincrease dynamic range of out-of-band signal components according toanother embodiment of the invention;

FIG. 16 is a diagrammatical sketch of an amplification system havingadjustable characteristics being controlled by the control system ofFIG. 5 according to the invention;

FIG. 17 is a diagrammatical sketch of an amplifier having adjustablecharacteristics being controlled by the control system of FIG. 10according to the invention;

FIG. 18 is a diagrammatical sketch an amplification system having afeedforward network with adjustable electrical characteristicscontrolled by the control system of FIG. 5 according to the invention;

FIG. 19 is a diagrammatical sketch of an amplification system having afeedforward network having adjustable characteristics being controlledby the control system of FIG. 10 according to the invention;

FIG. 20 is a diagrammatical sketch of an amplification system having acontrol system adapted to control the adjustable electricalcharacteristics of the feedforward network of FIG. 18;

FIG. 21 is a diagrammatical sketch of an amplification system having acontrol system controlling multiple components according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 5, an amplification system 100 is shown amplifying aninput signal fed thereto on a line 101. More particularly, the system100 provides an amplified output signal on a line 103. The system 100includes an amplifier 102, a control system 104, the details being shownin FIG. 7), and a predistorter 105, all arranged as shown. The inputsignal on line 101, in this embodiment, is a received CDMA signal. Thereceived signal has a predetermined, a priori known, bandwidth "BW";however, the carrier frequency f_(c) of such received signal may be anyone of a plurality of available carrier frequencies and is not known inadvance.

The amplifier 102 is biased to Class A/B, and thus has a non-linearamplification characteristic. Therefore, non-linear amplification by theamplifier 102 will introduce amplitude and phase distortion into theamplified output signal. Thus, passing a signal through the amplifier102, operating with a non-linear output power versus input powertransfer characteristic produces frequency components outside thebandwidth BW (that is, out-of-band frequency components).

In this illustrated embodiment, however, the output signal produced bythe amplifier 102 is fed, using the control system 104, to thepredistorter 105. The predistorter 105 has adjustable electricalcharacteristics, for example, adjustable bias characteristics andparameters. The predistorter 105 receives the input signal on line 101and the output of the control system 104, over line(s) 109. The outputof the predistorter 105 is fed to the amplifier 102. The predistorter105 has a non-linear gain versus input signal level characteristicselected in accordance with an out-of-band feedback control signal (thesignals over line(s) 109) to enable the amplification system 100 toprovide a substantially linear amplifier output power versus inputsignal power transfer characteristic to the input signal 101. Thus, inthe steady-state, the output on line 103 is an amplification of theinput signal on line 101 without, or with reduced, out-of-band frequencycomponents. As will be described, any out-of-band frequency energy inthe output signal on line 103, as the result of drift in the amplifier102, for example, is detected and is fed to the predistorter 105 usingthe control system 104 to enable the system 100 to again produce, in thesteady-state, an output signal on line 103 with little, or no,out-of-band frequency components.

More particularly, a feedback loop 107 is provided wherein the controlsystem 104 receives the output of the amplifier 102 and produces thefeedback control signal on line 109 for the predistorter 105. Thecontrol system 104 analyzes the signal produced by the amplifier 102 tolocate a carrier frequency having the bandwidth BW of the receivedsignal, here the carrier frequency of the input signal on line 101, andto produce the feedback control signal on line 109 related to the energyin the distortion frequency components (that is, the energy out of thebandwidth BW) detected in the output signal on line 103. In theillustrated embodiment, the control system 104 measures the energy ofthe distortion frequency components by measuring energy at a frequencyor frequencies offset from the carrier frequency (for example, atfrequencies 800 KHz and 1.25 MHz from the carrier frequency), themeasurement frequency(s) being outside of the bandwidth of the inputsignal. The feedback control signal on line 109 is coupled to thepredistorter 105 for adjusting characteristics of the predistorter 105(for example gain and phase, or predistorter bias points) and therebynull (that is, reduce) the energy in the out-of-band signals on line103.

Referring again to FIG. 5, in one embodiment, the control system 104heterodynes to baseband the amplified signal on line 103 with thecarrier frequency of the received signal and measures the energy in theoutput signal on line 103 at one or more predetermined offsets from thecarrier frequency. Referring also to FIGS. 6A-6C, the frequency spectrum18 of the input signal on line 101 is shown in FIG. 6A. The frequencyspectrum of the output signal on line 103, in a non-steady-statecondition, that is before correction, is shown in FIG. 6B to haveout-of-band frequency components 22a, 22b resulting from the non-linearoperation of amplifier 102. The frequency spectrum resulting fromheterodyning to baseband the output signal on line 103 with the carrierfrequency of the input signal is shown in FIG. 6C.

As shown in FIG. 6A, the input signal on line 101 is centered aboutcarrier frequency f_(c) and has an a priori known bandwidth BW. In thecase of a CDMA signal, BW will be 1.25 MHz. As shown in FIG. 6B,amplification by amplifier 102, prior to steady-state, introducesout-of-band distortion components 22a and 22b to the output signal online 103. The control system 104 heterodynes the amplified signal online 103 (FIG. 6B) to baseband, thus centering the signal about DC (zerofrequency) as shown in FIG. 6C. After heterodyning, the out-of-banddistortion components appear at frequencies greater than an offset ofBW/2 from DC or in the case of a CDMA signal at frequencies above 0.625MHz. The control system 104 produces control signals based on amount ofenergy measured at, for example, 0.625 MHz or other predeterminedfrequency offsets. That is, control system 104 produces control signalsbased on the amount of out-of-band energy in components 22a, 22b.

More particularly, and referring to FIG. 7, in one embodiment, thecontrol system 104 is shown in more detail and includes amicrocontroller 124 that controls a frequency synthesizer 126 toheterodyne (here, to bring down to baseband) the signal produced byamplifier 102 on line 103. A mixer 106 receives the output of thefrequency synthesizer 126 and the amplifier output on line 103, anddelivers its output to a bandpass filter 108 that eliminates in-bandfrequency components of the heterodyned signal to enhance resolution ofthe out-of-band distortion components. An amplifier 110 receives thefiltered signal and provides its amplified output to ananalog-to-digital converter 120, the digital output of which isdelivered for digital signal analysis by a digital signal processor(DSP) 122. The DSP is specially configured to effect a spectrum analysison the digital input signal from the analog-to-digital converter 120.The microcontroller 124, executing firmware instructions 128, queriesthe DSP 122 for the energy measurements at predetermined offsets. Themicrocontroller 124 analyzes past and present energy measurements toproduce control signals over lines 109 that adjust the electricalcharacteristics, for example, a phase and gain, of the predistorter 105.

Referring also to FIG. 8, in operation, the microprocessor instructions128 continuously monitor distortion levels by querying the DSP 122 formeasurement data describing the energy at offsets from the now basebandsignal center frequency (step 132). After determining whether thecurrent measurement process is operating satisfactorily (step 134) (thatis, distortion is reduced to predefined minimum levels for the system),by analyzing past and current measurements, the microprocessor producesthe control signals on lines 109 (step 136) that reduce or maintain thedistortion level. The control signals on lines 109 adjust differentelectrical characteristics, for example, the phase and amplitudecharacteristics of the predistorter 105 or bias characteristics of thepredistorter, to null any out-of-band frequency components 22a, 22b inthe output signal on line 103. It should be noted that reducingdistortion may require dynamic experimentation with differentcombinations of control signals before identifying a set of controlsignals that best minimize distortion.

Referring again to FIG. 7, in addition to generating control signals onlines 109, the microcontroller 124 executes instructions that controlthe frequency fed to mixer 106 by frequency synthesizer 126. Referringto FIG. 9, in operation, the microcontroller 124 uses the frequencysynthesizer 126 to incrementally sweep through the frequency spectrum tofind the carrier frequency f_(c).The microcontroller 124 initiates thesearch for the carrier frequency f_(c) by setting the frequencysynthesizer 126 to produce a low frequency (step 138). Themicrocontroller 124 queries the DSP 122 for a measure of the carrierenergy at this frequency (step 140). This corresponds to a DCmeasurement of the signal output of mixer 106. The microcontroller 124compares the energy measurement with the measurement of energy at apreviously selected carrier frequency produced by the frequencysynthesizer (step 142). If the comparison (step 142) indicates a steeprise (step 144) in energy. characteristic of a signal having apredefined bandwidth, the microcontroller 124 can freeze the frequencysynthesizer at this or a nearby frequency. If the comparison (step 142)does not indicate the presence of a signal (that is, very little energyin either the present or previous energy measurement), themicrocontroller 124 will increment the frequency produced by thefrequency synthesizer 126 (step 143). In a typical CDMA system, thefrequency synthesizer will be incremented in 50 KHz steps. (Other, orrandom, search patterns can also be used.) Finding the carrier frequencyusually needs only to be performed upon start-up as an allocatedfrequency usually remains constant. The search can be periodicallyrepeated, however, to ensure proper calibration. The results of thesearch can be stored to obviate the need for searching each time theequipment is start-up. The instructions of the microcontroller 124 canbe altered to search for different signals other than CDMA signals.

Referring to FIG. 10, in another particular embodiment, the controlsystem 104, here designated as control system 104', has an alternateconfiguration for reducing distortion in the amplification system.Control system 104' receives both the original input signal on line 101(FIG. 6A) and the amplifier output signal on line 103 having, in thenon-steady-state condition, distortion components introduced by theamplifier 102 (FIG. 6B). By mixing the original input signal on line 101with the signal on line 103 which can have distortion components, thecontrol system 104' quickly heterodynes the amplified signal on line 103to baseband without scanning the frequency spectrum to determine theinput signal's carrier frequency f_(c). That is, instead of searchingfor the carrier frequency of the input signal on line 101, the inputsignal itself serves as the signal for a mixer 106' (FIG. 12) in ahomodyne arrangement. In any event, the control system 104' thus locatesa frequency within the bandwidth (BW), here the center frequency of thereceived signal, by automatically homodyning, mixing, and filtering asprovided by mixer 106' and low pass filter 108 (FIG. 12). Mixing asignal in this manner, however, imposes a constraint upon the mixer usedby the control system.

More particularly, many mixers depend on a threshold amount of energy tomultiply signals without introducing distortion. For example, diodemixers introduce distortion into an output signal if the energy ineither of its two input signals falls below a level needed to keep themixer diodes operating in their linear region. Many signals, includingCDMA signals, sometimes fail to provide this minimum energy, therebyintroducing distortion.

Referring to FIG. 11, many mixers, such as a Gilbert Cell mixer, remainlinear even when the input signals have little energy. As shown, GilbertCell mixer 106' includes active devices configured as a four quadrantmultiplier biased into a linear operating region. These active devicesform a differential amplifier 176a-176b that drives dual differentialamplifiers 172a-172b and 174a-174b. The mixer output, on a line 177, isthus available for filter 108.

Referring to FIG. 12, an amplification system 101', using a homodyningmixer 106', is shown for measuring the energy in frequency bands of areceived signal, such signal having an allocated frequency bandwidth anda carrier frequency. The system 101' includes mixer 106' having activedevices configured as a four quadrant multiplier biased into a linearoperating region for enabling the mixer to handle low input signallevels. The mixer 106' receives a pair of signals, one of the signalsbeing the received signal (that is, the original input signal on line101) and the other signal, on line 103', being a portion of the outputon line 103 from a coupler 103". The output of mixer 106' is processed,as was the output of mixer 106 (FIG. 7) by the remaining components ofthe control system 104' which detect energy in a frequency band at apredetermined offset from the baseband carrier (center) frequency asdescribed above in connection with FIG. 7. Note that in an alternateembodiment of those illustrated in FIGS. 7 and 12, the DSP 122 (and itsrelated circuitry) can be replaced by bandpass filters, each adapted topass signals only at selected offsets from the center frequency. Othercircuitry would measure the energy from each filter and provide thatdata to the microprocessor.

Referring now to FIG. 13, the use of the four-quadrant linear multiplier(that is, mixer) 106' can pose a dynamic range problem. However,cancelling in-band frequencies to isolate the out-of-band distortioncomponents can increase the dynamic effective range of the mixer. Thus acancellation network 146, under microprocessor control, performs thisisolation function, thereby in effect, increasing the dynamic range ofthe mixer. The operation and structure of cancellation network 146 isillustrated in FIGS. 14 and 15.

Referring now to FIG. 14, one embodiment of the cancellation network 146is shown which uses a voltage controllable phase shifter 150 and avoltage controllable attenuator 148 to substantially cancel in-bandfrequency components in the amplifier output signal on line 103. Themicrocontroller 124 adjusts the phase shifter 150 and attenuator 148 tomodify the phase of a sample of the original input signal on line 101(FIG. 6A) by 180° and thereby null the in-band frequency components ofthe signal on line 103, from a coupler 149a, as they are coupled to theoutput of variable attenuator 148 using a coupler 149. Themicrocontroller 124 can repeatedly adjust the phase shifter 150 andattenuator 148 until the in-band's signal cancellation is at maximumlevel.

Referring to FIG. 15, an alternative embodiment of the cancellationnetwork 146' uses an automatic gain control element (AGC) 158, as iswell known in the field, to effectively increase the dynamic range ofthe mixer. The AGC 158 controls an amplifier 156 to hold the localoscillator (LO) input of mixer 106' over a line 159 constant so that thedown converted output of the mixer 106' is a linear function of theinput over line 159a and no longer a multiplicative function of theinputs to the cancellation network 146'. The AGC 158 also matches theoutputs of amplifiers 154 and 156. Phase and gain network 160 enablesthe microcontroller 124 to adjust the signal fed into mixer 106' andthereby increase dynamic range.

The control systems 104 and 104' can control a wide variety ofamplification system networks having adjustable characteristics otherthan predistorter 105. For example, in particular, referring to FIGS. 16and 17, corresponding to FIGS. 5 and 12, respectively, the controlsystem 104, 104' can control the amplification characteristics ofamplifier 102 by altering the amplifier's bias point(s). While apredistortion circuit is not shown, it can be advantageously employed tofurther reduce unwanted distortion. As described in co-pending U.S.application Ser. No. 09/057,380, filed Apr. 8, 1998, incorporatedherein, by reference, in its entirety, over long periods of time (forexample, hundreds of hours) amplifiers frequently exhibit a drift inoperating bias current. Amplification by an amplifier experiencing driftcan introduce out-of-band distortion components into a signal. Thecontrol system 104, 104' can generate control signals that control thebias of the amplifier based on out-of-band frequency energy tocompensate for amplifier bias current drift. This method of compensationis particularly useful in connection with MOSFET devices, and inparticular lateral MOSFETS where the gate bias is critical.

In addition, referring to FIGS. 18, 19, the control system 104, 104' canalso reduce distortion by adjusting the characteristics of a feedforwardnetwork 160. As noted with regard to FIGS. 16 and 17, a predistortercircuit can be advantageously used to further reduce unwanted distortioncomponents under the control of, for example, a microprocessor.Referring to FIG. 20, an amplification system 161 is illustrated whichreduces out-of-band frequency components of an input signal over line101 which after passing through Class A/B amplifier 102 has both in-bandfrequency components and out-of-band frequency components. Theamplification system includes a feedfoward network 160 having a combiner162 that receives a pair of signals: the first signal (FIG. 6A) over aline 161 from delay element 161a having the in-band frequency componentsand a second signal (FIG. 6B) over a line 163 coupled to the amplifier102 output, that has both in-band and out-of-band frequency components.Optimally, the combiner 162 subtracts the first signal from the secondsignal to produce a signal having only out-of-band frequency components.A variable gain-phase network 164, 166 receives the output of thecombiner 162 and applies its output to an error amplifier 168. Amplifier168 amplifies the out-of-band frequency components. A second combiner170 adds the output of amplifier 168 (that is, a signal havingout-of-band distortion components shifted by 180°) to the signal havingboth out-of-band and in-band frequency components from a delay 169.Ideally, combiner 170 produces an amplified signal substantially free ofout-of-band distortion components as is well known in the field.

However, as mentioned above, changes in the feedforward network 160components and the amplifier 102, over time, can reduce theeffectiveness of the feedforward network 160 in reducing distortion.Thus, the output of combiner 170 is coupled, in part, by a coupler 171to a feedback loop having control system 104. The control system 104,described previously, detects energy in the out-of-band frequencycomponents and produces a feedback control signal related to themeasured energy in those out-of-band frequency-components. The feedbackcontrol signals are coupled to and adjust, in this illustratedembodiment, the characteristics of the gain-phase network 164, 166 inaccordance with out-of-band frequency components.

As noted above, a predistortion circuit, as illustrated in FIGS. 5 and12, can be advantageously used to further reduce unwanted distortioncomponents under the control of, for example, the microprocessor 122 ofFIG. 20. In addition, regarding both the illustrative examples of FIGS.19 and 20, the microprocessor 122 can be used to adjust bias parametersof a predistorter, main amplifier 102, gain-phase circuitries or otherdevices to advantageously reduce distortions in the amplified outputsignal.

Referring now to FIG. 21, the control system 104 or 104' can controlmultiple components of an amplifier system to produce an overall reduceddistortion amplified output signal. As shown, the control system 104controls the predistorter 105, the bias point of the main amplifier 102,and the characteristics of the feedforward network 160. Thus, differentindividual amplification system networks (for example, the predistorter)combine to form a larger network (that is, predistorter and amplifierand feedforward network) having adjustable characteristics adjustablycontrolled by the control system in response to detected energy in theout-of-band frequency components.

Throughout this discussion it has been implicitly assumed that the inputsignal on line 101 was a single channel, bandwidth limited signal havinga carrier frequency which was not known in advance. The distortioncompensation circuitry described in connection, for example, with FIGS.7 and 20, can also be employed when the input signal is a multi-channelsignal, each channel having a bandwidth limited signal. When used withmulti-channel inputs, the compensation system finds one channel, andminimizes the out-of-band frequency components for that channel as ifthe other channel(s) did not exist. Thereafter, the settings used forthe one channel are used for all of the channels.

Thus the operative structure and method of operation of the FIGS. 7 and20 embodiments remain the same. It further appears not to matter whichchannel was minimized so that the frequency generator 126 searchpattern, established by microprocessor 124 can be the same as for asingle channel, that is, for example, can be a linear or a random sweep.

Additions, subtractions, and other modifications of the disclosedembodiments will be apparent to those practiced in the field and arewithin the spirit and scope of the appended claims.

What is claimed is:
 1. Apparatus for reducing out-of-band frequencycomponents of an RF signal having a carrier frequency which is not knownin advance, and having both in-band frequency components and the out-ofband frequency components, such apparatus comprising:a network foramplifying an input signal for producing said RF signal, said networkhaving adjustable electrical characteristics; and a control systemconnected to the network for locating a frequency within the bandwidthof the amplified RF signal and for detecting energy in the out-of bandfrequency components for producing a control signal related to theenergy in the out-of-band frequency components, such control signalbeing coupled to the network to adjust the electrical characteristics ofthe network and reduce the energy in the out-of-band frequencies.
 2. Theapparatus of claim 1, wherein the network comprises a predistorterhaving adjustable characteristics controlled by the control signal. 3.The apparatus of claim 1, wherein the network comprises an amplifierhaving adjustable characteristics controlled by the control signal. 4.The apparatus of claim 3, wherein at least one adjustable characteristiccomprises a bias point parameter of the amplifier.
 5. The apparatus ofclaim 1, wherein the network comprises a feedforward network.
 6. Theapparatus of claim 1, wherein the signal comprises a CDMA signal.
 7. Theapparatus of claim 1, further comprising a second network havingadjustable characteristics, the characteristics of the second networkalso being controlled by the control system.
 8. The apparatus of claim1, wherein the control system comprises a digital signal processor.
 9. Amethod of reducing out-of-band-frequency components introduced into anRF signal having in-band frequency components, having a carrierfrequency not known in advance, by a signal processing network withadjustable electrical characteristics, the method comprising:locating anin-band frequency component of the RF signal; detecting energy atfrequencies at a predetermined offset from the located in-band frequencycomponent; and adjusting network electrical characteristics based onsaid detected energy to reduce the out-of-band frequency energy.
 10. Themethod of claim 9, wherein locating the in-band frequency componentcomprises:measuring the energy at a first frequency; measuring theenergy at a second frequency; and determining whether the energymeasured at the second frequency exceeds the energy measured at thefirst frequency by more than a threshold.
 11. The method of claim 9,further comprising heterodyning the signal having out-of-band frequencyenergy.
 12. Apparatus for reducing distortion components introduced intoan input signal by passing such signal through an amplifier operatingwith a non-linear output signal versus input signal transfercharacteristic, such signal having a bandwidth centered about a carrierfrequency not known in advance, such distortion components being atfrequencies outside the bandwidth, the apparatus comprising:(A) apredistorter, connected to receive the input signal and having an outputcoupled to the amplifier, such predistorter having a predistorternon-linear output signal versus input signal transfer characteristicselectably adjustable in accordance with an out-of-band feedback controlsignal to provide a substantially linear amplifier output power versusinput signal power transfer characteristic; and (B) a feedback loopcomprising a control system connected to the amplifier output forlocating the carrier frequency of the input signal and for producing afeedback control signal related to energy in the distortion frequencycomponents outside the bandwidth of the amplified input signal, suchfeedback control signal being coupled to the predistorter for adjustingcharacteristics of the predistorter to reduce the energy in theout-of-band frequency components of the amplifier output.